1. Field of the Invention
The present invention relates to the estimation of the positioning errors of a nose cone radar and the drift in ground speed of an inertial unit with which an aircraft is equipped.
The matching of the referential system of an inertial unit to that of a radar (hereinafter called referential matching) is a matter of critical importance. For, in addition to the errors of the radar itself in its reference system, there are the errors pertaining to the conversion of these measurements into the reference system of the inertial unit. This is very critically important for the angular measurements of the radar.
To minimize the errors of positioning between the radar and the inertial unit of an aircraft, it is the common practice to use a method of calibration on the ground known as harmonization which is done by means of test patterns and an optical sighting system. This method of harmonization consists in matching the referential systems of the inertial unit and the radar as precisely as possible with respect to a reference trihedron linked to the aircraft.
This procedure of harmonization is lengthy and difficult to implement. Furthermore, it does not take account of the deformations of the structure of the aircraft in flight.
The correction of the drift in ground speed of the inertial unit is done by a periodic rematching by comparison between the position estimated by the inertial unit and the true position deduced from the passage of the aircraft through reference points having precisely known coordinates or by any other system of location such as a satellite navigation system.